使用SAX和dom4j解析XML文档

声明：类容为学习传智播客方立勋教学视频，总结。

一：SAX采用事件处理方式解析XML文档： 解析器 和 事件处理器（有多个处理器）

a:解析器可以使用JAXP的API创建，创建出SAX解析器后，就可以指定解析器去解析某个文档了。

b:解析器只要解析到xml文档的一个组成部分，就会调用时间处理器的一个方法，同时把当前解析到的内容作为方法的参数传递给事件处理器。

得到解析器是模版代码：

		// 获取sax解析工厂
		SAXParserFactory factory = SAXParserFactory.newInstance();
		// 获取sax解析器
		SAXParser sp = factory.newSAXParser();
		// 获取sax读取器
		XMLReader reader = sp.getXMLReader();
		// 设置内容处理器
		reader.setContentHandler(new TagValue());
		// 读取xml内容
		reader.parse("src/dom.xml");

 

我们的主要工作就是写事件处理器。

有两种方式：

a：实现ContentHandler接口

b：继承DefaultHandler类，覆盖我们需要的方法。
二：dom4j解析xml文档

模版开始代码：

    @Test  
    public void read() throws DocumentException{  
        SAXReader reader = new SAXReader();  
        Document doc = reader.read(new File("src/Book.xml"));  
          
        Element root = doc.getRootElement();  
        Element book = (Element) root.elements().get(1);  
        String value = book.element("书名").getText();  
        System.out.println(value);        
    }  

 写回文档的代码：

  

XMLWriter writer = new XMLWriter(new FileWriter("src/Book.xml"));  
writer.write(doc);  
writer.close();  

 

dom4j有一个提取根标签的方法，很不错。

官方的说明文档很详细，基本一看就会了。就不在赘述了。

下面叙述一点XPath。w3cschool上面有这方面的讲解。但是讲解最好的个人认为是：http://zvon.org/xxl/XPathTutorial/General_chi/examples.html

实例：

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.junit.BeforeClass;
import org.junit.Test;
import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.Locator;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;

/**
 * sax解析xml文档
 * 
 * @author forlab
 * @version 2012-12-19
 */
public class Sax {

	public static void main(String[] args) {
		try {
			ReadXml();
		} catch (ParserConfigurationException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SAXException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	@BeforeClass
	public static void setUpBeforeClass() throws Exception {
	}

	
	public static void ReadXml() throws ParserConfigurationException, SAXException,
			IOException {
		// 获取sax解析工厂
		SAXParserFactory factory = SAXParserFactory.newInstance();
		// 获取sax解析器
		SAXParser sp = factory.newSAXParser();
		// 获取sax读取器
		XMLReader reader = sp.getXMLReader();
		// 设置内容处理器
		BeanListHandler handler = new BeanListHandler();
		reader.setContentHandler(handler);
		// 读取xml内容
		reader.parse("src/dom.xml");
		List list = handler.getBooks();
	}
}

class ListHander implements ContentHandler {

	@Override
	public void setDocumentLocator(Locator locator) {
		// TODO Auto-generated method stub

	}

	@Override
	public void startDocument() throws SAXException {
		// TODO Auto-generated method stub

	}

	@Override
	public void endDocument() throws SAXException {
		// TODO Auto-generated method stub

	}

	@Override
	public void startPrefixMapping(String prefix, String uri)
			throws SAXException {
		// TODO Auto-generated method stub

	}

	@Override
	public void endPrefixMapping(String prefix) throws SAXException {
		// TODO Auto-generated method stub

	}

	@Override
	public void startElement(String uri, String localName, String qName,
			Attributes atts) throws SAXException {
		System.out.println("<"+qName+">");
		//获取元素节点的属性值
		for(int i=0;atts!=null && i<atts.getLength();i++){
			String attName = atts.getQName(i);
			String attValue = atts.getValue(i);
			System.out.println(attName+"="+attValue);
		}
	}

	@Override
	public void endElement(String uri, String localName, String qName)
			throws SAXException {
		System.out.println("<"+qName+">");
	}

	@Override
	public void characters(char[] ch, int start, int length)
			throws SAXException {
		// TODO Auto-generated method stub
		System.out.println(new String(ch, start, length));
	}

	@Override
	public void ignorableWhitespace(char[] ch, int start, int length)
			throws SAXException {
		// TODO Auto-generated method stub

	}

	@Override
	public void processingInstruction(String target, String data)
			throws SAXException {
		// TODO Auto-generated method stub

	}

	@Override
	public void skippedEntity(String name) throws SAXException {
		// TODO Auto-generated method stub

	}

}

//继承类代码实现更容易
class TagValue extends DefaultHandler {
	private String currentName;
	private int needNum = 1;
	private int currentNum;

	@Override
	public void startElement(String uri, String localName, String qName,
			Attributes atts) throws SAXException {
		// TODO Auto-generated method stub
		currentName = qName;
		if(currentName.equals("作者")){
			currentNum++;
		}
	}

	@Override
	public void endElement(String uri, String localName, String qName)
			throws SAXException {
		// TODO Auto-generated method stub
		currentName = null;
	}

	@Override
	public void characters(char[] ch, int start, int length)
			throws SAXException {
		// TODO Auto-generated method stub
		if ("作者".equals(currentName) && currentNum == needNum ) {
			System.out.println(new String(ch, start, length));
		}
	}
}

class BeanListHandler extends DefaultHandler{
    private List list = new ArrayList();
    private String currentTag;
    private Book book;
	@Override
	public void startElement(String uri, String localName, String qName,
			Attributes attributes) throws SAXException {
		currentTag = qName;
		if("书".equals(currentTag)){
			book = new Book();
		}
	}

	@Override
	public void endElement(String uri, String localName, String qName)
			throws SAXException {
		if("书".equals(qName)){list.add(book);
		book = null;
		}
		currentTag = null;
	}

	@Override
	public void characters(char[] ch, int start, int length)
			throws SAXException {
		System.out.println("内容="+new String(ch,start,length));
		if("书名".equals(currentTag)){
			String value = new String(ch,start,length);
			book.setName(value);
		}
		if("作者".equals(currentTag)){
			
			String value = new String(ch,start,length);
			book.setAuthor(value);
		}
		if("售价".equals(currentTag)){
			String value = new String(ch,start,length);
			book.setPrice(value);
		}
	}
	
  public List getBooks(){
	  return list;
  }
	
}

 

 

import java.io.File;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Node;
import org.dom4j.io.SAXReader;
import org.junit.BeforeClass;
import org.junit.Test;


/**
 * @author forlab
 * @version 2012-12-19
 */
public class Dom4j {

	@BeforeClass
	public static void setUpBeforeClass() throws Exception {
	}
	/**
	 * 利用xpath技术，查找dom.xml中name属性值为forlab的元素
	 * @throws DocumentException
	 */
	@Test
	public void valid() throws DocumentException{
		String username = "forlab";
		SAXReader reader = new SAXReader();
		Document document = reader.read(new File("src/dom.xml"));
		Node node = document.selectSingleNode("//作者[@name='"+username+"']");
		if(node==null){
			System.out.println("用户名或者密码错误!");
		}else{
			System.out.println("恭喜登陆成功!");
		}
	}
}

   相关资料：http://www.blogjava.net/junglesong/archive/2008/02/21/181196.html